1. Field of the Invention
This invention relates to a joint assembly for sealingly connecting the ends of a pair of sheet metal duct sections and more particularly to a joint assembly that includes a pair of frame members having flange portions secured to each other by angular corner pieces having rearwardly curved or displaced flange portions operable to facilitate an air-tight seal between the ends of the duct sections and the frame members.
2. Description of the Prior Art
U.S. Pat. No. 3,712,650 discloses a flange connection for connecting the ends of rectangular air conditioning ducts that includes flange portions each having a horizontal leg portion secured to the end portion of the duct and a vertical channel shaped leg for receiving the arm of an angular corner piece. A wall of the horizontal flange portion has a sloping intermediate portion that permits visual access to the bend areas between the adjacent walls of the duct and ends of the duct walls.
The angular corner pieces have arm portions which each extend into an opening in the vertical channel shaped flange. The arm portions are so dimensioned vertically that the lower surface of each arm abuts the lower wall of the horizontal flange. With this arrangement the end of the duct wall abuts or rests against the surface of the corner piece arm extending into the channel shaped opening.
Another joint assembly for connecting the ends of a pair of ducts is disclosed in German application No. P 25 56 167 filed Dec. 13, 1975, and includes a plurality of flange portions secured to the ends of the ducts and angular corner pieces positioned in vertically extending channel shaped openings in the respective flange portions to form a generally rectangular frame secured to the ends of the ducts. The flange portions each have a generally horizontal duct receiving leg and a vertical channel shaped leg. The duct receiving leg portion has a longitudinal opening for receiving the duct end wall and one wall of the vertically extending channel shaped leg has an inturned or inwardly rebent portion that forms a longitudinally extending lip spaced from the lower wall of the horizontal duct receiving leg. The duct end portion is arranged to extend into the space between the longitudinally extending lip and the lower wall of the horizontal duct receiving leg. In position, the duct end wall abuts the inner surface of the outer vertical wall of the upstanding channel shaped leg. The arm of the corner piece is arranged to extend into the opening above the inturned lip so that the corner piece arm portion is spaced from the duct end wall by the inturned lip portion. The corner pieces have arms with a curved configuration so that pairs of facing arms in adjacent frames are intended to exert a joinder pressure on the respective frame when the corner pieces are bolted to each other.
In the above joint assemblies, the duct end walls abut either the arms of the corner pieces or abut the inner surface of the frame channel shaped leg portion outer vertical wall. Where the end of the duct wall rests against the arm of the corner section, a space is provided between a substantial portion of the outer vertical wall of the channel shaped leg and the end of the duct wall. Where the end of the duct wall is positioned in the space between the inturned lip and the horizontal bottom wall, the duct end wall abuts a portion of the vertical wall of the frame section between the lip and the horizontal bottom wall. In either instance, irregularities on the surface of the duct or on the surface of the frame portions permit leakage of air from the duct through the flange connection. Positioning gasket material on the outer surface of the frame portions does not eliminate this air leakage since the leakage is occurring within the frame portions and around the duct end wall.
In German Offenlegungschrift No. 2,221,312 published Nov. 15, 1973 a fibrous gasket material is disclosed as positioned between the upper surface of the duct end portion and the under surface of the inturned rebent portion. French Pat. No. 1,363,255 discloses two pieces of sheet metal joined by a fold arrangement with a sealant engaged to the edge of one of the metal sheets. U.S. Pat. No. 3,246,918 discloses a flange connection in which sealing is achieved by the penetration of an end of a duct into a mastic.
One problem encountered with the joint assemblies of the prior art is the inability to form an air-tight seal around the duct end wall positioned oppositely of the vertical wall of the frame section adjacent the horizontal bottom wall of the frame section.
One proposed solution to this problem, as disclosed in the German OLS referred to above, is positioning a longitudinally extending gasket in the longitudinal space between the inturned rebent portion and the lower wall of the horizontal duct receiving leg. If when the duct end wall is inserted in the duct receiving leg portion, the gasket material is rolled up against the inner surface of the vertical wall of the channel shaped leg portion, an incomplete seal is formed around the end of the duct and the inner surface of the bottom wall of the duct receiving leg portion. Consequently, the end of the duct is substantially spaced from the inner vertical wall of the channel shaped leg portion. An air space is thus formed between the outside gasket on the outer surface of the frame portions and the duct edge because the outside gasket rests on the corner pieces and does not contact the duct edge. This permits air from the duct to flow around the end of the duct and between the outside surface of the duct and the under surface of the corner piece. Thus, air leaks from the ducts at the corners of the frame connecting the ducts.
There is need for a joint assembly that provides an effective corner seal between the duct end wall and the corner pieces that connect the adjacent flanges that form the joint frame. While it has been suggested by the prior art joint assemblies to utilize a longitudinally extending gasket in the flange portions to form a seal around the duct end portion in the flange portions, the gasket inside the flange portions does not prevent leakage around the corner pieces adjacent the ends of the flange portions. In addition, even with the use of an outside gasket on the corner pieces, unless the edge of the duct abuts the inner surface of the vertical wall of the flange portion, the outside gasket does not contact the end of the duct and air will leak around the end of the duct and between the duct and the corner piece beneath the outside gasket.